The Robot! He sounds good.

Superduper

Member (SA)
Sometime back, I was fortunate enough to find a Pioneer Disco Robo J-7. Some of you can find them in the trash where you live, but here in USA, they are like unicorns or Loch Ness, or Sasquatch... rumored to exist, people talk about them but no one has ever seen one. Well I did, and I bit immediately.

Upon arrival, I discovered that it was in pretty good condition, but has all the idiosyncratic issues common with this set:
  • Cassette Deck no longer working
  • Foam surrounds, on all 4 speakers, rotted out
  • But, most concerning, deteriorated tape button control panel membrane. Cheep-Azz Pioneer, damm them to h*ll for being so dang cheeeep!
No matter, I'm all in and determined to not only fix this thing up, but make it better.

First I rebelted the tape deck. It was a rather simple task. Years of experience and familiar with little tricks certainly helped. Otherwise, could have been a bit tedious for a first timer. Although the deck is simple, this is a good thing because it is rock solid reliable. No high effort mechanical levers run it... simply press the electric buttons and they work. FF, RW, Play and Stop. That simple. I like it! After rebelling, no tape speed adjustment was necessary which is a pleasant departure from norm. And I dare say, the deck sounds very good. Probably not the best in terms of hi-fi but I'm just guessing. They are pre-recorded goodwill tapes after all and not $60 metal tapes recorded on high end equipment. Although I can't say if the deck sounds as good as or better than the best existing boombox deck, I can definitely say that it sound better than many many other decks.

Ok, so during my initial testing, I found that the unit can get pretty loud, but it sounded horrible. Lots of distortion and buzzing. No wonder, the speakers, all of them, are rotted out. Need to refoam them all.
dr-3.jpg

Here is one of the speakers sitting next to a Sanyo M9990 driver. It's TINY, but LOOK at the magnet. These drivers weighs like 5 of the Sanyo driver (ok, I'm exaggerating, but not by much). As for magnet strength, lets put it this way: when removing the mounting screws, the screwdriver kept getting sucked up by the magnet (think movies with some poor metal accessorized sap pasted onto an MRI machine turned on). Them are serious magnets!
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Here they are, ready to foam. I ordered rubber surrounds, hoping to never do this again. Unfortunately, they sent me foam surrounds. Well, I can't wait so I'm gonna install them. Foam should last like 20 years anyhow so I guess that's good enough for now. When I got something tore down, I'm not exactly a patient person. I also wish the interior diameter of the new surrounds was slightly smaller because the overlap on the cone is a bit small to my liking but I guess I'll just have to be careful. Luckily these speakers are ported and not sealed which would put more stress on the cones/surrounds.
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One done, 3 more to go.
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All done, ready to reinstall.
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Now, on to the crappy fake button membrane.... Unfortunately, time is not kind to this material, as the chemical nature gets unstable. They look like fungus infested toe nails, all alligator skin cracked. But underneath are true good quality switches. Could there be a better solution?
dr-1.jpg

Well, I ordered a couple replacement membranes from a fella in HK. Paid big bucks (big to me). I took one look and said to myself..... uh no. Not gonna use them. If anyone needs one (or both), hit me up, you can have 'em at my cost. Instead, I took to the drawing board to get ideas. I wanted a permanent elegant solution. Not some cheap plastic membrane that belongs on an appliance (think Microwave here).
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OK, I'm moving quick so it seems like this is just days right? No, this is months in the process. But here are my prototypes, for checking fit, quality, etc.
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Well, unfortunately, I didn't account for the deck door swing and while they fit with the door closed, there is interference when door opens. I need to increase the top bevel and rethink the thickness of the panels. Material feel is good. They are made of nylon with a somewhat sandblasted feel to them but not sandpaper rough -- hard to describe. Buttons work well and fit well into the panel receptacles. Tried operating the switches and they work great! Yes! Anyhow, now that I have proof of concept, I went back to the CAD drawing board to make adjustments. Unfortunately, I can't figure out how to do that so I had to remake them all over again fresh. I initially thought I would paint the pieces to suit but decided to instead order colored pieces. Here are the new pieces:
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Success! Fit is good, Look is good. Now time to install onto the top panel. Works perfectly! Buttons/switches all operate with slight light pressure. Feels professional and no longer like a toy. I also like the new color scheme compared to original. I like the way it looks. Check it! I have one extra set of this black/yellow/green/red assembly -- PM me if you are interested in doing the same thing (I also have the two reproduction membranes too that I mentioned above if anyone needs).
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Happy to say that this thing is surprisingly loud. It's one of my loudest sets. The amp board contains 2 LA4440 chips (typically used in cars etc) mounted onto a huge heat sink. Datasheet says "typically" 19wpc in BTL mode but at something like 13.2v. As this box is 15V on batteries and probably higher on AC, it's not a stretch to say that this unit puts out 22-25wpc rms easily. I've heard other reviews saying these aren't hifi. But all I can say is that it sounds very very good. Bass is decent because those speakers were designed with high X-Max cones & ported too, and it clearly has no trouble reproducing highs. The only downside is that there is no tone controls. But guess what, while tone controls are usually the first things I want to tweak when I turn on a boombox, surprisingly on this one, the audio is very balanced and I don't find myself looking to adjust it to any significant extent -- sound great as it. Although the tuner looks like an afterthought, and I say this because of the tiny scale, I discovered that it is actually a good tuner, much better than a lot of boomboxes. The small scale probably more a function of no real estate to put a true decent tuner dial scale.

Anyhow, I'm happy as a clam now, and listening as I work! I think this is going to be my new workhorse for music while I work. There's nothing not to like about this thing.

Honorable mentions: I want to thank Eric (Caution) for helping me make up a paint template so I could reproduce the 109db legend on the grill as I wanted to paint the grills due to some blemishes I didn't like.

A lot more work not mentioned went into this restoration, which I'll save for maybe an e-book that I'll write about this adventure. I may also install a bluetooth receiver before I'm done. However, I have no desire to add any disco lites to it. It's a shame that these are so rare here. It has instantly become one of my favorites, and because I have so many boomboxes, that's saying something.
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T-STER

Member (SA)
Jul 14, 2014
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UK
Wow what an amazing resto, this is well beyond the realms of a rebelt and some grills painted, this was a lot of work. It turned out fantastic. As you say its a shame these are so rare as I'd love to hear/see One.
 

deech

Member (SA)
Jan 11, 2012
680
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Athens Greece
Super Duper This Pioneer Robot is such a unique unit .
Great detailed restoration , it must have been time consuming but well worth it.
 

Fatdog

Well-Known Member
Staff member
May 3, 2009
10,898
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This thread is the stuff of legends. That's a most excellent restoration, Norm! :cool: :bow: :hooray:
 

Superduper

Member (SA)
Hisrudeness said:
Great resto Superduper. I remember a post where a collector restored the membrane . Think it was an Aussie collector.

Not surprised it sounds decent, it’s a pioneer after all.
I can never gauge from pictures but how tall is this thing?

Here it is

https://boomboxery.com/forum/index.php/topic/23851-dirty-pioneer-disco-robo-gets-the-treatment/
Hey Rudy, I purchased exactly those membranes. I know my text is long so it's easy to skip through on to the pictures, but if you read it, you'll discover that I even purchased Two of them, just in case. But.... after looking at them, I didn't like them. Didn't match the quality of the rest of the boombox. Would be like having wheely quality equalizers in an SK-900. I didn't care if it looked original or not, if original meant THAT! So the are spares for me (or someone else) but in truth, these new true buttons will now last forever.

Height: About 22" tall without handle. About 27" tall with handle. Weight, approximately 28 pounds or so, I'm guessing. However, very easy to carry because handle is extremely sturdy, feels like strong metal or metal clad over plastic. And the pivot joint, like a precision engineered swivel -- almost zero play except for it's intended range of motion. At no point does the handle feel bouncy, even if you try (and strong enough to shake the boombox by the handle). And although carrying a large boombox (like an M90) or larger can become cumbersome and needs to be balanced, this thing is more like carrying a bucket with handle, so easy.
 

BoomboxLover48

Member (SA)
Dec 3, 2010
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Chicago, IL
Great work by the Master Boombox Wizard ... Great Norm! :rock:

The speakers should be all full range and was wondering if we can add a crossover to include tweeters it should sound even better.

Panny 466 has two dual cone full range speakers. I was always surprised by the sound quality it gives with full range speakers.

I wish I could see some pictures of the interior. The amp board, cassette section and all. I would think there is a lot of empty space in the Robot. Little curious to see how the interior looks like.

~Royce
 

blu_fuz

Moderator
Staff member
Jun 3, 2009
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Well look at you posting some kick ass refurb projects! The robo is looking good and I love the red surrounds and new buttons. Nice work.
 

Superduper

Member (SA)
Ok, as I posted my thread late last night, here is more work that I did on the Disco Robo.

Here is the amplifier module. Very clean layout, massive heatsink to protect the two LA4440 amp chips. Well designed layout and all harnesses are on connectors so very easy to remove if necessary. As I was waiting for the commercial 3D printing service to produce my new panel setup and was waiting for the new speaker surrounds, I decided to go ahead and recap the amplifier. Why not? Might as well do a full resto for future reliability as well.
dr-amp1.jpg

The heatsink is removed from the board. Note how clean the board is. As the rear is vented and the heatsink cooled through convection, this tells me that the unit has not received much use. Convection cooled systems always suffer from lots of dust deposited from the flow of air through the system. Heatsink compound is dried out so that will be replaced. Discovered that the heatsink has lots of scratches on it from manufacturing. The factory didn't bother to polish out the scratches. To maximize heat transfer and contact area, I polished out the micro scratches on the mating surfaces to the amp chips.
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Board recapped. One of the easier boards to do. All voltage specs were upgraded for greater margin of safety.
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Heatsink ready to go back on.
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Completed board, ready to reinstall into the set.
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Board nested back in place. Note the heavy gauge power cables & neat cabling arrangement. Those power cables are entering home audio gear territory! And we aren't talking lamp cord either (hear that Lasonic?). These are quality mil-spec cables.
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Install complete. Checkout the speaker cables, now plugged back in. Yep, those look like beefy 18 guage cables too. What other boombox has speaker cables like that? None. Even the M90, C100, etc all use smallish 22 gauge cables. Cables like these are usually only found on car and home audio gear. The speaker drivers are 2-ohms each in series making 4-ohms/side. The speaker system itself adds a considerable amount of weight to the set and yep, you need heavy cables to get the most out of them.
dr-amp7.jpg
 

Superduper

Member (SA)
BoomboxLover48 said:
I wish I could see some pictures of the interior. The amp board, cassette section and all. I would think there is a lot of empty space in the Robot. Little curious to see how the interior looks like.

~Royce
Very little empty space. Almost every inch was accounted for. Under that top "hat" is the cassette mechanism and cassette circuit board and the mixer panel. On the backside is the amplifier board and above that, the tuner board. Along both edges on backside are the two battery tubes. Situated on the front side is all speakers of course. Then there is the bottom which houses the power supply and all the I/O jacks and circuits.





Well look at you posting some kick ass refurb projects! The robo is looking good and I love the red surrounds and new buttons. Nice work.
Joe, I have lost interest some time ago working on boomboxes because it is very difficult for me to do most things nowadays. Loss of finger strength and dexterity due to rapidly progressing rheumatoid arthritis is doing me in. But for some reason, maybe because of its novelty, or because it is totally different... I somehow pushed through the pain and forgot about all my ailments, lol.
 

Hisrudeness

Member (SA)
Jan 1, 2014
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Nice to see something different posted now and then. A great addition to your collection.

You must be very pleased with this score Norm? I would've been giddy with excitement.
 

Superduper

Member (SA)
Hisrudeness said:
Nice to see something different posted now and then. A great addition to your collection.

You must be very pleased with this score Norm? I would've been giddy with excitement.
These don't exist in the states. I have looked for one of these for over a decade and never saw any come up for sale. If they did, I must've missed them. Any existing is probably imported. But in answer to your question, yes, I seldom post whole articles like this anymore but it is exactly the excitement of this acquisition that carried me through the resto. I'll try to find a spot to place a bluetooth receiver and once that's done, it'll be time to enjoy it.
 

Reli

Member (SA)
Dec 24, 2010
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Congrats on finishing this! Those buttons look very good quality.

LA4440 amplifier, very nice......That's the same chip that's in the MX720, but your Pioneer has two!
 

Superduper

Member (SA)
I've been listening to this... it's crazy how far the sound carries. I had it pounding in downstairs family room. I went up stairs. I went to the other end of the house upstairs. I hid in the restroom doing my business. The sound is everywhere! Who needs an FM transmitter when you got this? It's the ultimate party box if you want to disturb, frustrate and annoy the heck outta everyone, :clap: :-O :-D . It's friggen crazy! The bass is not low like a kaboom but it definitely has strong bass and solid. Good midrange, and excellent treble. Royce, don't need no tweeters with this thing, treble is not lacking. In fact, if you wanna, you can listen to and be very very happy with classical music too.

The amps do work very hard with these woofs. After about 15 minutes workout, the heatsink was pumping out radiant heat. Feeling the sinks from behind the amplifier chips, it was quite hot. Not too hot to touch, because the heatsink is fairly large but you can definitely feel the heat where the chips were and then it bleeds off and gets cooler on the heatsink the further you go. I think I'm gonna beef up this heatsink so it can draw more heat away and be more effective.

Oh, and lots of people look at this thing and think they see equalizer on the front panel. It is not. That is a mixer panel. You can mix line-in, radio, microphone, and tape. There is an echo feature for crazies (have no clue why anyone would wanna do that to the sound). There is also a slider for tape speed pitch. You can use any or all of those at the same friggen time, if you are crazy of course. But I suppose it could come in handy if someone wants to talk using microphone, and then cue in some sappy background music to go with the monologue. And there is a line-out too, of course, in case you wanna record what you are mixing or if for some reason, you want to send output to another amplifier (what???). Yep, this is a fun box.